In many applications a voltage regulator is required to provide a voltage within a predetermined range. Some circuits are subject to uncertain and undesirable functioning and even irreparable damage if an input power supply fall outside a certain range.
A functional block diagram of a prior art power supply apparatus 10 is shown in FIG. 1. The apparatus 10 generally includes a power converter 12 coupled with a transformer 14 that is coupled with an output rectifier 16. The output rectifier 16 is coupled with an output capacitor 19 at an output Vout. A regulation circuit 15 comprising an opto-coupler 17 and a voltage reference and error amplifier 18 is coupled between the voltage converter 12 and the output Vout. The power converter 12 is configured to receive an unregulated DC voltage signal. The unregulated DC voltage signal is coupled to the transformer 14. The transformer 14 includes a primary 14P and a secondary 14S. The unregulated DC voltage signal drives the primary 14P to produce an intermediate voltage signal. The intermediate voltage signal comprises a stepped-up or stepped-down voltage signal derived from the voltage signal that drove the primary 14P. The intermediate voltage signal is coupled to the output rectifier 16. The output rectifier 16 rectifies the intermediate voltage signal to produce a regulated DC output voltage signal. A feedback signal provided by the opto-coupler 17 is coupled to the power converter for regulating the output voltage Vout.
A schematic diagram of a prior art regulated power supply 100 is shown in FIG. 1A. The power supply 100 includes a converter circuit 102 coupled with a transformer 140. The transformer 140 is coupled with an output circuit 106. The converter circuit 102 includes a capacitor 110 coupled across an input Vin and coupled with a primary 140P1 and 140P2 of the transformer 140. A primary switch 112A and an auxiliary switch 112B are coupled with the primary 140P1 and 140P2 respectively. A pulse width modulator (PWM) module 130 is coupled with a gate of the primary switch 112A. The output circuit 106 includes an output rectifying diode 146 and a load or an output capacitor 150 coupled across a secondary 140S of the transformer 140. The power supply 100 can include a voltage regulating circuit including optical coupler circuit 108 and a voltage reference and error amplifier 109. The power supply 100 uses the PWM module 130 to alter a duty cycle of the primary switch 112A. The optical coupler circuit 108 in cooperation with the voltage reference and error amplifier 109 provides feedback to the PWM module 130. The PWM module 130 accordingly adjusts the duty cycle of the primary switch 112A to compensate for any variances in an output voltage Vout. Very often the point of failure for the power supply 100 is the opto-coupler 108. The opto-coupler 108 and the voltage reference and error amplifier 109 increase production cost of the power supply 100.
Accordingly, it is desirable to create a regulated power supply to greatly reduce a point of failure and to reduce production cost.